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Beni Kumonryu with Tumour


Introduction is copied from the tumour Article


Tumors happen in fish, just like in other animals and humans. The cause of many of the tumours and malformations found among Koi are for the most part poorly known, because studies involving fish are few and far between. The financial incentives for studies on fish are just not there. Certain malformations are caused by injuries.  Tumors occur on nearly all organs or tissues. Some tumors are caused by various ingredients in the diet. There is also a suspicion that viruses may cause certain tumors, similar to the megaloblastic growth in cells like with Lymphocystis and Lymphosarcoma. Certain chemicals are also known to be carcinogenic and may cause tumors. Tumors on the skin are very obvious and some resolve itself over time, given an increase in temperature and optimal water conditions.

Most tumors do not appear to be fatal to the fish, but may lead to complications over time. I have witnessed many fish that developed a tumor and the situation seems to stabilize after the initial disfiguring growth. In such a case the fish then leads a normal life for weeks, months and in some cases many years. In some cases a tumor will appear and then continue to grow until the skin rapture or the sheer volume of the growth will actually inhibit the normal functioning of vital organs. When the skin raptures, the end result will inevitably be a massive bacterial infection.

In very rare cases, the tumor will actually protrude through the ruptured skin and manifest itself as a rubbery, raised, dark red growth, resembling an open, raised sore.

When a tumor develops around an organ in the body cavity and continues to grow, the end result is normally a blockage of some kind and the fish will, during the final stages, exhibit symptoms very similar to dropsy shortly before death.

The above reasons for tumors are valid, but more and more data are accumulating to implicate environmental agents as important for carcinogenesis in humans, animals and fish. Many of these agents enter the natural waters and come in contact with fish and invertebrates. These agents can be of natural, industrial and agricultural origin. They are numerous and can include natural agents such as UV light. Other agents include crude oil, various soluble metals and their salts, petroleum wastes, DDT, other pesticides, benzyl, arsenic, domestic wastes, herbicides, aromatic amines, and various components of effluent from mines, industry, and dyestuffs. The mechanisms by which these environmental agents act to generate neoplasia are presently unknown. That they probably do act additively and even synergistically in conjunction with multiple host factors is well known in mammals and certainly should be similar in fish.

There are a few studies available on the impact of genetics on the development of cancer/tumors in fish, but I could not find a specific study referring to the common carp or to Koi. There are however references to the impact of in-breeding and line-breeding in fish and the conclusion that I could reach is that the limited genetic pool in Koi breeding must surely be a contributing factor to the frequent occurrence of tumors in Koi, especially those tumors that occur on young fish.

There are various reasons for malformations in koi and therefore one should not suspect a tumor at first glance. Impacted eggs or the start of dropsy may also be the cause of bloating. A tumor can therefore only accurately be diagnosed through an autopsy. There are however certain ways to be reasonably sure that a tumor is present in a fish. The first indication is a swelling that occurs. This swelling is mostly on one side of the fish, and not a symmetrical, even swelling for example of the whole abdominal area. The second difference to impacted eggs and dropsy is that while the bloated area is normally soft, a tumor will feel like a distinctive hard lump inside the fish when firmly touched.

There is no cure for a tumor. The only solution is to remove it surgically. The removal of a tumor in normal tissue can be successful but the procedure to remove an abdominal tumor is very invasive and such a procedure mostly result in the fish dying from bacterial infection within a few days after the operation. I must haste to add that some successes have been reported, but exceptional skill is necessary where the tumor has engulfed some vital organs.

The Beni Kumonryu.

The following case study is actually very graphic and disturbing. It is however in the interest of all to understand the absolute finality of a case, once a tumour has been confirmed. A fish may live for years with a tumour, but it may also kill the fish within a month or two.

In this instance, I bought the Beni Kumonryu for my personal collection. I have been searching for years for a nice one and in particular the one that Kate McGill calls “incomplete”. I love a white face and white dorsal area, although I knew it may change.

I kept the fish in quarantine for two months and after the necessary tests, released it in my main pond. Soon I noticed a slight bulge on the side of the fish. It was obvious that a tumour had developed but I hoped it was one that will offer the fish a considerable time of quality life. Boy, I was in for an unpleasant surprise!

The poor fish was getting worse on a daily basis.  I watched the progress in alarm. The skin was absolutely stretched and there has developed stretch marks on the belly just behind the pectoral fins. I also noticed the indentations on both sides of the dorsal fin. The Beni Kumonryu is actually eating well, but losing weight. Maybe it is to sustain the huge tumour inside?

Mostly fish die from a tumour because of the tendency to engulf the intestines. In this case, the only symptoms that the fish displayed were the incredible swelling and a difficulty to swim.

Eventually the dreaded day arrived that I was convinced that the quality of life was deteriorating to such an extent that I could not let the situation continue. It was not a good day for me. As in every case, it was necessary to try and determine what exactly went wrong. How could a fish remain active and eat well while carrying such a massive burden?

This is the full story. Heartbreaking.


The start of the problem 06 November 2010. It is obviously a tumour.


Photo on 3 December 2010. Fish is eating well but the tumour size has increased dramatically. Note that the fish is losing weight.


Photo on 14 December. The fish eats well but is now very skinny. One can actually see the “ribs”

Tumour is now so big the fish battles to swim around. I have to make a decision today!


Very tough but necessary. Euthanizing.


Note the stretch marks and the size of the belly



Ready for autopsy




The killer revealed.


Note where the tumour has developed. It is alongside the intestines, explaining why the fish was able to survive up to now. The swim bladder remained intact.


Close-up of the tumour




Surprisingly, nothing wrong with any of the organs.


Look at the weight of the tumour!


43% of body weight!


Tumour bisected.


The example above is a very graphic illustration of the misfortune that may befall any koi in the hobbyists care, and the reasons for the occurrence of the tumour may never be known

When the hobbyist is confronted with the reality that one of the koi has a tumour, the question about what to do next should be addressed. The following advice was posted on the Koivet forum By Don Chandler, aka “KoiCop”, Global Moderator of the Koivet forum on 29 January 2009.

"Now that you know it is a tumor, here comes the rough part. We know from experience what is going to happen next so let me give you a thumbnail sketch of what to expect.

The tumor will continue to grow and as it does, it is consuming vital nutrients from the blood that would otherwise be used to keep the fish alive in normal conditions. The fish's organs will attempt to compensate for this but will not be able to do so. The net result is that the tumor will ultimately rob the organs of the blood nutrients they need and the organs will begin to fail with the most notable being the liver and kidneys (the blood organs). As the organs fail, the fish loses the ability to generate red blood cells with the result that it becomes anemic. With an anemic condition, the fish also loses the ability to transport O2 to the body and this causes further degradation in the fish's condition. This now becomes an ugly cycle.

As I note with every tumor case, the next piece of evidence of the decline of the fish's health will be the condition of the gills. As the fish becomes more anemic, the gills will pale noticeably and turn a uniform pale, pale pink. This will tell you that the fish no longer has the ability to generate red blood cells and is in fact, suffocating from the lack of O2 uptake. When I see this happen, it is time to euthanize the fish humanly. If you do not, the fish will become very lethargic and seek a quiet place near the surface or a well-oxygenated area of the pond in an attempt to save its strength and take up more O2. Then it will pass what appears to be quietly as the organs fail completely and the heart stops."

Last Updated on Monday, 14 March 2011 22:26